The ADRs are able to detect most faults. In a case like that, the ELAC and FAC and/or FMGC will eliminate the erroneous ADR. The only effect of that would be that one display may be wrong, and autoland is downgraded CAT 3 SINGLE.
When all three are erroneous, and in some cases when two are off, the system may not be able to identify the the ADR(s) that are u/s. On both PDF's a SPEED LIM flag will appear. The ELACS will also trigger a NAV ADR DISAGREE caution.